The present invention relates to electrical discharge processing of polymer material, in strip form, particularly for increasing the aptitude of the strip material to receive adherent products.
Polymers in strip form are of considerable industrial interest. Strips constituted by a continuous film are used for wrapping food products, for manufacture of photographic films and as printing supports. Strips of porous polymeric material or fabric are also widely used.
For use, the strips must be adapted to ink reception, to coating or to complexing. In order that the treatments may be carried out under good conditions, it is necessary to subject the polymer strip material to a preliminary treatment improving surface adhesivity. For this purpose there have been used processing by oxidizing solutions, by flame and by corona discharge.
It is an object of the invention to provide an improved processing method which does not require the use of toxic chemical substances and authorize high processing speeds.
According to an aspect of the invention the strip is passed successively at a first emplacement where electrical charges are deposited on one surface of the strip, then at a second emplacement where an arc is created sliding along said surface of the strip between electrodes subjected to alternating high voltage.
It is possible to use various methods to deposit the charges on the strip. In particular, it is possible to use charged particle-emitting radio-elements. However, a much preferable solution consists of depositing the charges on the strip by corona discharge between a conductive support bearing the strip and a wire electrode parallel to the support and brought to a negative voltage with respect to the latter.
According to another aspect of the invention, an apparatus utilized for processing polymer strip material in strip form by electrical discharge comprises a support arranged to receive the strip; a wire electrode substantially parallel to the support, whose radius of curvature is very much smaller than that of the support; means for establishing a voltage between the support and the electrode which is selected for creating a current by corona effect depositing charges on the strip; electrode means located at an emplacement for the passage of the strip downstream of the wire electrode; and means for establishing between said electrode means an alternating voltage creating an arc sliding along that surface of the strip which has received the charges.
When the strip is of great width, it is possible to provide more than two electrodes distributed across the strip and associated in pairs with AC generators.
The invention will be better understood from the following description of an apparatus which constitutes a particular embodiment, given by way of example only.